According to Google OS, users can also add custom gadgets to Google Calendar, however the method is slightly different that it is for Gmail.

Here are some simple steps to add custom gadgets to Google Calendar

How To Add Custom Gadgets To Google Calendar

Step 1: Find a gadget that you want to add to Google Calendar and get the URL for it, you can find more info on getting the URL for a gadget in our earlier tutorial for Gmail.

Step 2: You will now have to create a new URL based on this format http://www.google.com/calendar/render?gadgeturl=GADGET_XML_FILE, where you will have to replace the GADGET_XML_FILE with the URL for the gadget.

Interesting method to add gadgets in Google Calendar. Do you also know how to delete them again? I added the Hello World gadget as available in the Google developer guide, but now want to delete it and that does not seem possible?